This invention generally relates to systems for warning the drivers of vehicles of a road hazard. More particularly, this invention relates to such a system wherein a class of vehicle, such as an emergency vehicle, broadcasts a radio signal at a fixed frequency for receipt by radio receiving units in private vehicles. Specifically, this invention relates to such a system in which each class of road hazard broadcasts a differently coded signal at the same frequency and activates warning devices in the private vehicles.
Emergency vehicles such as police cars, fire engines and ambulances have the right-of-way while responding to calls for assistance. In order to signal their approach to the public, such vehicles have traditionally used sirens and flashing lights. When a motorist in a private vehicle is alerted by the sound or light, he is required to yield the right-of-way. However, the problem of alerting the public by the use of such devices has become acute in the past few years. More and more people drive with their automobile windows up year round as automobile air conditioning has become commonplace. In addition, automobile music systems have become extremely popular and efficient. The net result is that the average driver receives very little audio input from the outside environment, thus rendering the use of sirens ineffectual. To further complicate the matter, flashing lights have never been especially effective in congested urban areas where lines of sight tend to be relatively short. In addition, despite the questionable effectiveness of sirens as warning devices, deaf persons in many states are under serious driving limitations because they cannot hear sirens. The net result of these factors has been a serious upsurge in collisions involving emergency vehicles and a general slow down in the ability of such vehicles to quickly respond to a call. Emergency vehicles are only a part of the problem faced by drivers without adequate warning. The general term road hazards can be used to include such problems as emergency vehicles, construction sites, railway trains, school zones and others.
Systems of this type are not unknown in the prior art and the following U.S. Patents are believed to illustratethe state of the art; U.S. Pat. Nos. 3,233,217; 3,293,600; 3,371,278; 3,441,858; 3,673,560; 3,760,349; 3,772,641; 3,854,119; and 3,909,826. None of the prior art systems have met with success, the major problem being one of complexity in dealing with a plurality of road hazards and the resulting cost of the entire system. For example, the system of U.S. Pat. No. 3,233,217 requires a very complex receiver to distinguish the multiple tones transmitted from ultiple hazard sources. Further, a false trigger signal gives no indication of being such.
I have solved these problems by my invention of a relatively simple system which requires only a very simple receiver. Each road hazard has assigned to it a unique pulse length coded identification signature. Police cars may use a dot-dot code, fire trucks a dot-dash-dot and construction projections a dash-dash, for example. Thus, each hazard has associated with it a transmitter which will transmit only one coded signal. The receivers in private vehicles are set to receive the common radio frequency carrier signal. The coded pulses, when received, are further modulated to cause a light to flash on and off in the code pattern and an audible signal to sound in the same code pattern. Thus, any coding complexity is built into the transmitters, while all the receivers may be identical yet respond to a plurality of different source signals.